Plastic parts are becoming more popular in a variety of manufactured items. Plastic parts provide cost and weight savings along with flexible design capability. Low surface energy plastics, such as polyolefins, are favored for use in many manufactured articles because of their cost, design and processing advantages. Many manufactured articles contain parts manufactured from different materials because of the different functions and operating requirements of the parts. Some parts are preferably manufactured from low surface energy plastics and others are manufactured from high surface energy plastics, metal, wood and/or glass.
Assembly of manufactured articles utilizing adhesives is advantageous because adhesives offer design and process flexibility. Isocyanate functional adhesive systems (often referred to as polyurethane adhesives) are popular adhesive systems for bonding a variety of substrates because polyisocyanate based adhesives bond well to a large number of substrates. Isocyanate functional adhesives systems can be formulated to to provide a wide variety of properties depending on the substrates and the use of the manufactured articles.
Low energy plastic surfaces typically require some kind of surface treatment to facilitate bonding of isocyanate functional adhesive systems to such surfaces. Such treatments include one or more of flame treatment, corona discharge treatment, chemical etching of the surface and/or primer application. Typical primer systems are utilized in processes wherein the primer is applied, the solvent carrier is allowed to volatilized away and then the adhesive is applied to the surface of the substrate. Known systems for bonding low surface energy plastic parts together or to other substrates typically allow for a relatively short open time between application of the primer and application of the adhesive. Examples of these systems are found in
EP 149,856 and U.S. Pat. No. 5,576,558, both incorporated herein by reference. Open time as used in this context refers to the time period after the solvent volatilizes off wherein the primer still links up to the adhesive system. Link up as used refers to chemical bonding of an adhesive to functional groups of the adhesive.
Low energy surface plastic parts are frequently utilized on automobiles, for instance as interior parts and bumper facia. Sheet molding compound is utilized in body parts and can be a difficult surface to bond to. Many manufacturers including automobile manufacturers do not like to have primers used in assembly plants because automobile workers are exposed to the solvent vapors and because environmental and safety regulations may require solvent removal and venting systems. Thus the use of primers in assembly operations can add cost and health and safety concerns to assembly plants. What is desirable are primers having a long open time thereby allowing application to substrates at a time and location remote from the assembly operations. In the context of automobile manufacture this means that component parts are primed in the plant of the component supplier and then shipped to the plant where the automobiles are assembled. Commonly owned patent application U.S. Ser. No. 12/033,420 filed Feb. 19, 2008 and Patent Cooperation Treaty Application PCT/U.S. Ser. No. 08/054,273 titled “One Component Glass Primer Including Oxazoladine” disclose a long open time primer system useful for linking polyisocyanate functional adhesive systems to glass, incorporated herein by incorporated herein by reference. Long open time primer systems for linking isocyanate functional adhesive systems to low energy plastic surfaces are not disclosed in these applications.
What is needed is a primer system that is capable of linking an isocyanate functional adhesive system to a low surface energy substrate which has a long open time, up to 90 days or longer. What is further needed is primer systems that can also be used on a variety of other substrates and which can be used in bonding low surface energy plastic substrates and other substrates, such as glass, metal, coated metal and plastic substrates which have relatively high surface energies.